1. Field of the Invention
The invention relates to a device for connecting in parallel transistors in very high frequencies and particularly those which are to be placed between an input line and and an output line arranged on two parallel conductive planes. The invention also relates to the use of such a device in a very high frequency and high power amplifier, for example 500 watts.
2. Description of the Prior Art
At very high frequencies, particularly above 1 gigahertz, transistors are frequently placed in load circuits insulating the collectors from earth. It is therefore necessary to insulate from earth the rear face of the transistor substrate (that opposite the face carrying the base and emitter electrodes).
In the case of a high power transistor, particularly above a few dozen watts, it becomes imperative to dissipate the heat given off during the operation of the transistor. A beryllium oxide plate is then placed between the earth and the rear face of the transistor substrate. Beryllium oxide simultaneously has a good insulating capacity, a good thermal conductivity and a thermal expansion coefficient which is relatively close to that of silicon. However, limitations are placed in this direction by the size of the useable beryllium oxide plates in the case of very high power transistors which in practice are constituted by a plurality of parallel-connected monolithic transistors (chips). Thus, during the welding of the chip to its support there is a risk of cracks or faults due to the very considerable difference in the thermal expansion coefficient between the beryllium oxide and the copper of the support. Moreover, in the case where several transistor chips are used with the same number of different substrates placed on the same beryllium oxide plate difficulties are encountered in the collective welding thereof and for making the parallel connections, without risking undesirable mixtures.
The invention makes it possible to solve most of these difficulties.